1. Field of the Invention
This invention relates to a method and an apparatus for detecting the abnormality of electric equipment, especially for a rotating electric machine such as an electric motor, a generator and so on, in particular, relates to a method and an apparatus for detecting the abnormality caused by the insulation aging of a stator winding.
2. Description of the Prior Art
Recently, the scale of a plant in an industry has generally been enlarging, and electric equipment such as a gas insulated system (hereinafter referred to as GIS) and a rotating electric machine, too, has been becoming larger in size, and the number of the installation of it has also been enlarging accordingly.
Because high reliability is required in such electric equipment, it is needed to surely practice the maintenance and the inspection of such equipment to prevent a sudden accident such as a dielectric breakdown. Besides, the greater part of the electric equipment manufactured during the high economic growth period in Japan has been operated for more than twenty-five years, then it is very highly requested to continuously keep supervising on it for preventing a sudden accident while it is operated.
Conventionally, there has been used an electrical method as a method for judging the insulation aging of electric equipment, for example, as regards the stator of a rotating electric machine, which electrical method imposes a high voltage on the winding of the rotating electric machine after the operation of the machine was stopped, and measures the electrical characteristics of the stator such as insulation resistance, AC current, dielectric loss angles, partial discharge and the like to estimate the degree of the aging of insulators in each part.
However, for making the judgement about the aging by the use of such a conventional method, it is required to stop the operation of electric equipment, and consequently, a great deal of time, labor and expenditure are required. Furthermore, the method has a defect that it is difficult to practice the judging tests of aging frequently. And it has another defect that it cannot fully cope with a case where the aging rapidly advances.
Accordingly, there is a prior art apparatus disclosed in the Japanese Patent Gazette No. 68852/92 (Hei. 4) for eliminating the problems described above. This apparatus provides a sensor electrode made of a metal material in the neighborhood of the stator coil in a slot, and connects a partial discharge measuring instrument to the sensor electrode for supervising the insulation aging during the operation of the electric equipment. Besides, Japanese Unexamined Patent Application Published under No. 296672/92 (Hei. 4) discloses an abnormality detecting apparatus which detects the high frequency signals induced by the partial discharge generated in its stator winding and propagated through the stator winding by the use of a temperature detector provided at a place adjoining the stator winding for detecting the abnormality of the winding of the stator.
FIG. 1 is a sectional view showing a main part of a prior art corona detecting apparatus for a high voltage rotating electric machine, which is disclosed in, for example, Japanese Patent Gazette No. 68852/92 (Hei 4). In the figure, reference numeral 3 designates a stator core, reference numeral 4 designates a stator winding, reference numeral 6 designates a slot, reference numeral 100 designates a stator winding conductor, reference numeral 101 designates a main insulating layer, reference numeral 102 designates a low resistance coated film which is provided on the surface of the main insulating layer 101, reference numeral 103 designates an inter-layers separating segment, reference numeral 104 designates a sensing electrode, reference numeral 106 designates a lead, and reference numeral 107 designates a corona measuring instrument. The sensing electrode 104 made of a metal material is electrically connected with the low resistance coated film 102 in the slot 6 of the stator core 3. The corona detecting apparatus supervises the insulation aging during the operation of the rotating electric machine by providing the sensing electrode 104 between the stator windings 4 housed in the slot 6 through the inter-layers separating segment 103 and by connecting the lead 106 drawn out of the sensing electrode 104 to the corona measuring instrument 107.
FIG. 2 is a sectional view showing the main part of another example of a prior art corona detecting apparatus. In this apparatus, the low resistance coated film 102 is divided in to parts 108 and 109, and one part 109 of them is contacted with the sensing electrode 104.
Next, the operation will be described thereof.
When insulation aging is happened in the high voltage rotating electric machines, which are shown in FIG. 1 and FIG. 2, partial discharge is generated at the main insulating layer 101 between the stator winding conductor 100 and the low resistance coated film 102. Because the sensing electrode 104, which is made of a metal material, is electrically connected with the low resistance coated film 102 in the slot 6, the partial electric discharge generated during the operation of the rotating electric machine can be detected by the sensing electrode 104.
Moreover, the apparatus shown in FIG. 2 is composed so as to divide the low resistance coated film 102 into the parts 108 and 109, and so as to contact the sensing electrode 104 with one part 109 of them. Consequently, the generated partial discharge can be detected from the part 109 of the low resistance coated film 102, which part 109 is insulated from the stator core 3, even if the part 108 of the low resistance coated film 102 is contacted with the stator core 3 electrically.
Furthermore, FIG. 3 illustrates a block diagram showing a prior art abnormality detecting apparatus for a rotating electric machine disclosed in Japanese Unexamined Patent Application Published under No. 296672/92 (Hei. 4). The drawing also illustrates a rotating electric machine partially broken away for showing the position of a partial discharge sensor which is installed in the proximity of stator windings.
In the drawing, the stator windings 4 are housed in the slot 6 formed in the stator core 3 which is fixed to a stator frame (not shown). The stator windings 4 are composed of two windings, upper one and lower one, and fixed by a wedge 7. A partial discharge sensor 9 is composed of, for example, a temperature detecting element 8a and lead wires 8b. and the sensor 9 is inserted between the two, the upper and the lower, stator windings 4 in a predetermined slot 6. The lead wires 19 of the partial discharge sensor 9 are connected with an abnormality determining circuit 110 through a temperature measuring instrument 22. The lead wires 19 are connected with the abnormality determining circuit 110 further through a filter 23 and a partial discharge measuring instrument 24. An alarm unit 11, an abnormality displaying unit 29 and an interface circuit 112 are also connected with the abnormality determining circuit 110.
Next, the operation of the prior art abnormality detecting apparatus shown in FIG. 3 will be described.
When an abnormality due to the insulation aging of the stator windings 4 happens, partial discharge is generated in the stator windings 4 and a high frequency current flows in the windings 4. The high frequency current generated by the discharge is propagated to the partial discharge sensor 9, too, which is connected with the upper and lower stator windings 4 electromagnetically, and the current is inputted into the filter 23. Since the partial discharge signal is a high frequency signal having a frequency more than several Khz, the filter 23 eliminates low frequency signals to be used in temperature measurement and inputs only the high frequency component of the discharge signal to the partial discharge measuring instrument 24. The partial discharge measuring instrument 24 analyses the inputted signal to measure a discharge characteristic, and outputs the discharge characteristic to the abnormality determining circuit 110. If the abnormality determining circuit 110 determines the situation to be abnormal, the circuit 110 outputs alarm signals to the alarm unit 11 and the abnormality displaying unit 29.
Generally speaking, while electric equipment is operated, many radio noises accompanied by the operation are generated. For example, in many generators having used for more than 15-20 years, the insulation abnormalities of which generators are needed to be supervised, the exciters of the generators, which supply field current to the rotors of the generators, supply DC current to the rotors through the slip rings of the generators. In these slip rings, arc discharge is generated in some contact states of their slipping surfaces, and radio noises are, in turn, generated. Furthermore, in a thyristor exciter, pulse-shaped thyristor noises are superposed on the exciting current of it. The exciters and the slip rings thus become generation sources of radio noises.
Moreover, the charging caused by the static electricity of steam turbines and the charging caused by the shaft induced current accompanied by the generation of electricity and the like are generated in the rotors. For the sake of discharging the charges of the rotors, the construction to provide grounding brushes to the shafts of the rotors is generally used for discharging the charges to the ground. However, arc discharge is generated in some contact states of the slipping surfaces of the grounding brushes, and radio noises are generated during this discharging, too. These radio noises show the resembled frequency characteristics to those of electromagnetic wave signals caused by void discharge generated in the main insulating layers 101 of the stator windings 4 shown in FIG. 1 and FIG. 2.
Also, radio noises generated in isolated-phase buses, various kinds of radio communication waves, broadcast waves and so forth invade into power stations from transmission system sides. These radio noises are often detected by the sensor which detects the partial discharge, too. In particular, being a high sensitivity sensor to high frequency signals, the partial discharge sensor 9 shown in FIG. 3 shows the characteristic of detection of the radio noises, too.
These radio noises are detected in stronger strength than that of the partial discharge signals. Besides, the frequencies of the radio noises exist in a near zone to those of the partial discharge signals, and the fact makes the detection of the partial discharge during the operation of electric equipment very difficult.
Because the conventional abnormality detecting method for electric equipment, and the conventional abnormality detecting apparatus for a rotating electric machine are constructed as described above, they have had no regard to the radio noises generated during the operation of them.
Also, even if an operator tries to detect the signals generated by the partial discharge during the operation of them, the obtained measurement results would contains the radio noises because of the impossibility of separating the partial discharge from the radio noises. Consequently, the conventional abnormality detecting method and apparatus have a problem that the accuracy of its abnormality detection is resulted to be very low.